1. Technical Field
The present invention relates to a vehicle occupant safety apparatus and, in particular, to a vehicle seat belt system including a seat belt webbing height adjuster and a pretensioner for taking up slack in the seat belt in the event of a vehicle collision.
2. Description of the Prior Art
Vehicle seat belt systems use seat belt webbing to restrain movement of a vehicle occupant. It is known to include a pretensioner in such a system. In the event of vehicle deceleration above a predetermined threshold level, such as occurs in a vehicle collision, the pretensioner is actuated to tension the belt webbing and to take up slack in the belt webbing.
It is also known to include a manually adjustable seat belt webbing height adjuster in a seat belt system. The belt webbing passes through a. seat belt webbing guide or D-ring that is supported on the height adjuster at a location adjacent to the shoulder of the vehicle occupant. The height adjuster enables the vehicle occupant to set the vertical position of the D-ring to one of several vertically spaced locking positions. In some height adjusters, the D-ring can, at times, be positioned vertically between locking positions.
Some seat belt systems include both a pretensioner and a height adjuster. When the pretensioner is actuated, the tensioned belt webbing exerts a strong downward force on the D-ring. If the pretensioner is actuated when the D-ring is not at a locking position, the D-ring is pulled downward along the height adjuster until it locks. It is desirable to ensure that the D-ring locks at the next available downward locking position and does not skip past one or more locking positions before engaging.
U.S. Pat. No. 5,794,977 describes a height adjuster which has two columns of projections in a rail affixed to the vehicle side structure. The height adjuster also has two corresponding latches which are engageable with the projections to lock the height adjuster. The latches and projections are staggered so as to prevent skipping past one or more locking positions before engaging.
U.S. Pat. No. 5,167,428 describes a height adjuster having a single column of vertically spaced openings in a rail, and a carriage having a pair of vertically spaced pins engageable in the openings. In this height adjuster, a lever must be actuated to pull the pins out of the openings in order to adjust the carriage upward along the rail.